Brush holder for dynamoelectric machines



April 7, 1959 A. FISHER BRUSH HOLDER FOR DYNAMOELECTRIC MACHINES Filed Jan. 31, 1956 2 Sheets-Sheet 1 Lllll lllII [five/7 to?" A/ec 56/76)? y /um fi w H/ls Attorney A ril 7, 1959 A. FISHER 2,881,3 9

BRUSH HOLDER FOR DYNAMOELECTRIC MACHINES Filed Jan. 31, 1956 2 Sheets-Sheet 2 Fig. 4

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United States Patent BRUSH HOLDER FOR DYNAMOELECTRIC MACHINES Alec Fisher, Erie, Pa., assignor to General Electric Company, a corporation of New York Application January 31, 1956, Serial No. 562,436

1 Claim. (Cl. 310-246) This invention relates to dynamo-electric machinery and more particularly to brush holders for electric motors and generators having commutators and slip rings.

The general use of longitudinally coiled tension springs for holding commutator brushes against the commutator in motors and generators is known in the art. Such constructions frequently utilize a longitudinally coiled spring attached to the brush holder at one end and terminating at the distal end in a self-winding coiled volute. The outer periphery of the volute is commonly disposed in engagement with the outer end of the brush and as the brush wears, the volute rerolls itself, maintaining a substantially constant pressure on the brush. The volute, as commonly applied, engages the brush near the leading edge thereof and the forces on the brush are thereby applied insuch sense that the brush is not urged toward the reaction surface and is inclined to chatter on the commutator with resulting undesirable effects. The springs have a tendency to creep further toward the leading edge of the brush, aggravating the chattering condition. Another undesirable effect is that the brushes are difiicult to remove from brush holders utilizing springs of the aforementioned type and it is often necessary to remove the spring itself before removing the brush to prevent damage to the spring and injury to the operator.

In the present disclosure, a brush assembly is shown which overcomes many of the disadvantages of prior commutator brush holders by providing a third class lever pivotally connected to the brush holder at the outer end and having the opposite end engaging the outer surface of the brush. A substantially constant pressure spring which terminates in a volute at one end in which each elemental increment along its length has substantially the same natural radius of curvature in its relaxed condition attached to the fixed brush holders has the distal end engaging a point on the lever intermediate the point of contact of the lever with the brush and the point where the lever is connected to the brush holder. The force of the spring is applied to the brush through the lever by connecting the volute end of the spring to the brush holder and the straight portion of the spring to the lever. This is a reversal of the position in which a spring of this type is usually used and several advantages result. For example, to remove the brush, the lever may be completely rotated out of contact with the brush and into a position completely out of the way without damage to the spring. By proper angular relationship between the lever and the brush, the lever applies a force of constant magnitude to the brush in such a sense as to urge the brush into engagement with the reaction surface of the brush holder as well as toward the commutator, thereby holding the brush in firm engagement with the reaction surface of the brush holder as well as toward the commutator and reducing the tendencyof the brush to chatter throughout the life of the'brush.

Specifically, an object of this invention is to provide a brush holder having a spring which applies pressure to the brush through a lever which may be swung completely free of the brush and, in the latter position, be urged by the spring away from the brush.

Another object of the invention is to provide a brush holder having a spring which applies constant pressure to the brush, the pressure force having a sense which holds the brush against the reaction surface of the brush casing in a manner to prevent brush chatter.

A further object of the invention is to provide a brush holder wherein the force applying means applies a substantially constant force to the brush in a direction toward the commutator and toward the reaction surface throughout the life of the brush.

A still further object of this invention is to provide a brush holder which is simple in construction, economical to manufacture, and simple and eiiicient to use.

With the above and other objects in view, the present invention consists of the combination and arrangement of parts hereinafter more fully described, illustrated in the accompanying drawings and more particularly pointed out in the appended claim, it being understood that changes may be made in the form, size, proportions, and minor details of construction without departing from the spirit or sacrificing any of the advantages of the invention.

In the drawings:

Fig. 1 is a side elevational view partly in cross section showing a brush holder according to the invention;

Fig. 2 is a top view of the brush holder shown in Fig. 1.

Fig. 3 is an isometric view of the brush holder and commutator shown in Figs. 1 and 2;

Fig. 4 is an enlarged view of the spring shown in Figs. 1 and 2;

Fig. 5 is an enlarged view of another embodiment of an attaching device for fastening the spring to a transverse member; and

Fig. 6 is a diagram illustrating the operation of the brush holder.

Now with more specific reference to the drawings, a brush holder is shown by way of example having a body 10 bored at 12. The bore 12 receives a rod 13 attached to a fixed frame. A slot 11 is cut in the end of the body 10 and communicates with the bore 12. The ends of the body 10 adjacent the bore 12 are drilled and one of the,

ends tapped to receive a bolt 14 which clamps the brush holder in place and against rotation on the rod 13 in a conventional manner. The brush holder has an opening 15 therethrough which receives a brush 16. The brush 16 slidably and snugly fits in the opening 15. An inner end surface 17 conforms to an outer peripheral surface 68 of a commutator 69 which rotates in the direction of the arrow shown thereon. An outer surface 24 of the brush 16 is inclined toward the commutator 69 and toward a lever 18 preferably at an angle of approximately thirty degrees so that the lever 18 will transmit a force to the brush 16 having a component toward the rod 13 of sufiicient magnitude to urge the upper end of the brush 16 toward a reaction surface 19.

Ears 20 are integrally connected to the brush holder at 22 and extend outwardly in parallel spaced relation. The lever 18 is pivotally connected to the ears 20 at 21. The lever 18 has a brush engaging end 23 and a handle portion 25 extending upwardly therefrom which is convenient to be grasped by the hand of the operator when it is desired to remove the lever pressure from the brush 16. The lever 18 has a bifurcated end portion terminating in two spaced legs 26 between which a distal end 30 of a spring 27 is disposed.

The spring 27 is supported on a sleeve 50. The sleeve 50 is freely rotatable on a pin 28 and wrapped there-- 3 the pin 28 rest in notches 70. The pin 31 extends transversely of the lever 18 and rests in notches 33 and 34. In its stressed position, the distal end 30 will be substantially unwound from the volute of the spring 27 and in the position shown, the spring 27 will be under tension and exert a downward force on the lever 18, urging the end 23 to swing around the pivot point 21, thereby causing the lever 18 to operate in the manner of a third class lever to urge the brush 16 downward and toward the reaction surface 19. This force, when combined with the frictional force on the brush 16 caused by the rotation of the commutator 69 in the direction indicated by the arrow, will urge the entire leading surface of the brush 16 to firmly engage the reaction surface 19 and, thereby, eliminate any tendency of the brush 16 to chatter.

As the commutator 69 wears away the brush 16 and thus shortens it, the outer surface 24 will move progressively toward the commutator 69 until the brush 16 reaches the dotted line position 40 and the lever 18 reaches the position 41. During this time, the volute will rewind itself on the sleeve 50, exerting a substantially constant pressure on the pin 31 as the brush 16 wears. At this point, the lever 18 will be in the dotted line position 41 and the spring 27 will still be applying a pressure on the upper surface of the brush 16 through the lever 18 substantially equal to the pressure exerted before the brush 18 was worn short.

In the example shown, the pivot point 21 of the lever 18 is so disposed that the angle made by a line 60 pass ing through the pivot point 21 of the lever 18 and the point of contact of the lever 18 on the brush 16 when the brush 16 has not been worn with a line 62 through the pivot point 21 and the point of contact of the lever 18 with the brush 16 when the brush 16 is half worn out is substantially equal to the angle made by a line passing through the pivot point 21 and through the point of contact of the lever 18 with the brush 16 when the brush 16 is worn to minimum length and the line 62.

Fig. 6 is a diagram showing the brush 16 first in its unworn position relative to the pivot 21, then in semiworn position, and finally in fully worn position. The pivot 21 is spaced from the brush 16 and is approximately half way between the maximum and minimum position of the outer surface 24 of the brush 16. The position of the pin 28 is disposed so that angle M is equal to angle N and R equals R Since the spring 27 exerts a substantially equal force on the lever 18 in all positions, then the force F is equal for all positions of the brush 16. Therefore,

Since FNXR=F2R2 and F21R1=FN1R, then FN=FN1- The component of F in line with the longitudinal axis of the brush 16 is equal to F and F and since angle M equals angle N, then F =F When the lever 18 is in the position B, that is, the semi-worn position, the force in line with F will be equal to F cos 90=F The force on the brush 16 at each end of the travel is equal to F cos of one-half the angle between the maximum and minium positions or equal to angle M or angle N. In Fig. 6, this angle is about fifteen degrees so that a variation of .96 F to 1.0 F will be obtained as the brush 16 moves through its travel. Throughout the life of the brush and in each case illustrated, the component of pressure against the back of the brush holder, that is, the reaction surface, will be substantially constant since the resolution of forces produced by the brush pressure F on surface AA related to top brush angle E is practically identical for all positions of the brush outer end.

When it is desired to remove the brush 16 for repair, replacement, or inspection, it is merely necessary for the operator to grasp the handle portion 25 and swing the lever 18 back to the dotted line position 42. A stop 45 may be so located that the pin 31 will be moved slightly past the position 43 and will be on the outside of a line passed through the pivot point 21 and the pin 28. The resulting overcenter toggle action from the force exerted by the spring 27 on the lever 18 will urge the lever 18 further back, the lever 18 will tend to swing further backward, and lower end 44 will engage the stop 45. Therefore, the lever 18 will be held firmly in the cocked position 42 shown and the operator will have both hands free to remove the brush 16 without the danger to himself of injury by the spring 27. Furthermore, the spring 27 will not be overstressed by this procedure.

In the embodiment of the invention shown in Fig. 4, a constant tension spring 217 is shown having its volute end 129 tightly coiled on a pin 128 which corresponds to the pin 28 in Fig. 1. The volute has a distal end 130 attached to a pin 131 by inserting the end through a slot 132 therein and anchoring it by soldering, brazing,

or other well known fastening means instead of fastening fastening means and the eyelet 232 is adapted to receive a pin 231.

The foregoing specification sets forth the invention in its preferred practical forms but the structure shown is capable of modification within a range of equivalents without departing from the invention which is to be understood is broadly novel as is commensurate with the appended claim.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

A brush holder for a dynamoelectric machine comprising a casing having walls defining an opening for receiving a carbon brush, one of said walls comprising areaction surface against which said brush bears when pressed into contact with a commutator, an outwardly protruding extension on said casing, a lever pivotally mounted on said extension and being of a length sufliclent to permit its free end to engage a surface on said brush shaped to an angle of approximately 30 with a" plane passing perpendicularly through the brush axis, a constant tension spring wound in a volute and mounted at one end on said casing and removably attached at its other end to said lever, said spring having a portion be pivoted away from the brush and held in place against said stop member by the over-center action of said spring to thereby permit unimpeded replacement of said brush.

References Cited in the file of this patent UNITED STATES PATENTS 852,705 Conlee May 7, 1907 932,309 McHugh Aug. 24, 1909 967,527 Knight Aug. 16, 1910 2,532,827 Thomas Dec. 5, 1950 2,695,968 Welch et a1. Nov. 30, 1954 2,804,558 7 Bauroth Aug. 27, 1957 

